I. Field of the Invention
This invention relates to a method and apparatus for forming crosspieces of a universal joint and, in particular, to a universal seal crosspiece having the rough form hot or warm forged and the trunnions extruded to their final form thereby maintaining the grain flow of the forged part.
II. Description of the Prior Art
Manufacturers are constantly seeking improved and less expensive methods of manufacturing spiders or crosses for universal joints used in automotive drive shafts. The strict requirements set by manufacturers of automatic transmissions for the automobile industry require the manufacturers of components to constantly improve the accuracy of the rough shapes for universal joint crosspieces or tripods. Traditionally, the spiders have been formed by a hot forging process. However, considerable machining and grinding was required to attain the necessary size, shape and surface finish of the trunnions. This machining resulted in a waste of material but also disrupted the grain flow of the part reducing the life of the part. Moreover, the additional machining steps increased the cost of manufacturing the part while resulting in a loss of raw material of up to 30%. In more recent times, attempts have been made to manufacture the crosses with less machining of the formed part. Complete extrusion of the spider in multi-piece dies has been utilized in an attempt to reduce costs by eliminating machining. These parts are extruded from a cylindrical slug into a multi-piece die to form the trunnions of the spider. Extrusion of the complete spider limits the configuration of the part. Uniform surfaces and die volumes must be maintained since it is difficult to fill corners and remote portions of the die under the uniform material flow during extrusion. Cold extrusion requires that the hub of the crosspiece be symmetrical so as to allow full extrusion of the trunnions forming the crosspiece or tripod. Although additional machining and therefore waste of materials is eliminated, extrusion of the complete part is still more expensive than forging the component. Moreover, the grain flow of the extruded part is highly distorted although the grain is not interrupted.